Method for fabricating ceramic matrix composite components

ABSTRACT

A method for fabricating a component according to an example of the present disclosure includes the steps of depositing a stoichiometric precursor layer onto a preform, and densifying the preform by depositing a matrix material onto the stoichiometric precursor layer. An alternate method and a component are also disclosed.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. application Ser. No.15/687,625 filed on Aug. 28, 2017, now U.S. patent Ser. No. 10/801,108.

BACKGROUND

This disclosure relates to a method of fabricating components, and inparticular, ceramic matrix composite (CMC) components.

CMC components typically comprise ceramic reinforcements, such asfibers, in a ceramic matrix phase. CMC components can withstand hightemperatures and oxidative environments due to their materialproperties, high strength and creep resistance, high thermalconductivity, and relatively low weight. An example CMC componentcomprises silicon carbide reinforcement embedded in a silicon carbidematrix material.

Various techniques are used to fabricate CMC components. For example, apreform comprising reinforcements is infiltrated with a matrix material.The composition of the matrix material affects the properties of the CMCcomponent. In turn, the composition of the matrix material can beinfluenced by the method of depositing the matrix material onto thepreform.

SUMMARY

A method for fabricating a component according to an example of thepresent disclosure includes the steps of depositing a stoichiometricprecursor layer onto a preform, and densifying the preform by depositinga matrix material onto the stoichiometric precursor layer.

In a further embodiment according to any of the foregoing embodiments,the preform comprises silicon carbide fibers.

In a further embodiment according to any of the foregoing embodiments,the stoichiometric precursor layer is silicon carbide, and wherein theratio of silicon to carbon in the stoichiometric precursor layer isapproximately one.

In a further embodiment according to any of the foregoing embodiments,the matrix material is silicon carbide and has a ratio of silicon atomsto carbon atoms, and the ratio is approximately one.

In a further embodiment according to any of the foregoing embodiments,the step of depositing the stoichiometric precursor layer onto thepreform is accomplished by an atomic layer deposition process.

In a further embodiment according to any of the foregoing embodiments,the step of densifying the preform is accomplished by a chemical vaporinfiltration process.

In a further embodiment according to any of the foregoing embodiments,the matrix material comprises one or more constituents, and the methodfurther comprises the steps of determining the ratio of the one or moreconstituents to one another, and comparing the ratio to thestoichiometric ratio of the matrix material.

In a further embodiment according to any of the foregoing embodiments,the depositing step and the densifying step are performed in the samereactor.

Another method of fabricating a component according to an example of thepresent disclosure includes the steps of arranging one or more preformsin a reactor, providing a silicon-containing precursor to the reactorsuch that the silicon-containing precursor adsorbs onto the one or morepreforms, providing a carbon-containing precursor to the reactor suchthat the carbon-containing precursor reacts with the silicon-containingprecursor to form a stoichiometric precursor layer, wherein the ratio ofsilicon atoms to carbon atoms in the stoichiometric precursor layer isapproximately one, and providing at least one silicon carbide precursorto the reactor to densify the one or more preforms by depositing asilicon carbide matrix onto the stoichiometric precursor layer.

In a further embodiment according to any of the foregoing embodiments,the silicon carbide matrix has a ratio of silicon atoms to carbon atoms,and the ratio is approximately one.

In a further embodiment according to any of the foregoing embodiments,the silicon-containing precursor includes one of Cl₂SiH₂, SiH₄, ClSiH₃,and Si₂H₆ and the carbon-containing precursor includes one of CH₄(methane), C₂H₆ (ethane), C₃H₈ (propane), C₂H₂ (acetylene), and C₂H₄(ethylene).

In a further embodiment according to any of the foregoing embodiments,the at least one silicon carbide precursor includes a first precursorand a second precursor, and the first precursor is methyltrichlorosilane(MTS) and the second precursor is hydrogen (H₂).

In a further embodiment according to any of the foregoing embodiments,the method further comprises the step of vacuuming the reactor after thestep of providing the silicon-containing precursor to the reactor toremove excess silicon-containing precursor from the reactor.

In a further embodiment according to any of the foregoing embodiments,the method further comprises the step of vacuuming the reactor after thestep of providing the carbon-containing precursor to the reactor toremove excess carbon-containing precursor from the reactor.

In a further embodiment according to any of the foregoing embodiments,wherein the reactor includes an exhaust valve, and wherein the exhaustvalve is closed during the step of providing the silicon-containingprecursor to the reactor and the step of providing the carbon-containingprecursor to the reactor, and the exhaust valve is open during the stepof providing at least one silicon-carbide precursor to the reactor.

In a further embodiment according to any of the foregoing embodiments,the one or more preforms comprise silicon carbide fibers.

In a further embodiment according to any of the foregoing embodiments,the silicon carbide fibers are coated with a boron nitride interfacialcoating.

In a further embodiment according to any of the foregoing embodiments,the silicon carbon fibers have a unidirectional orientation with respectto one another.

In a further embodiment according to any of the foregoing embodiments,further including the step of determining the ratio of silicon atoms tocarbon atoms in the silicon carbide matrix, and comparing the ratio toone.

A ceramic matrix composite component according to an example of thepresent disclosure is formed by a process comprising the steps ofdepositing a stoichiometric precursor layer onto a preform anddensifying the preform by depositing a matrix material onto thestoichiometric precursor layer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A schematically shows a ceramic matrix composite (CMC) component.

FIG. 1B schematically shows a close-up view of the CMC component.

FIG. 2 schematically shows a method of fabricating the CMC component.

FIG. 3 schematically shows a furnace for fabricating the CMC component.

FIG. 4 schematically shows a CMC component during fabrication.

FIG. 5 schematically shows a method depositing a stoichiometricprecursor layer onto a preform.

FIG. 6 schematically shows a method of densifying a preform with astoichiometric precursor layer to form a CMC component.

FIG. 7 schematically shows a CMC component during the densifying step.

DETAILED DESCRIPTION

FIGS. 1A-1B schematically illustrate a ceramic matrix composite (CMC)component 20 for hot sections of gas turbine engines, which operate attemperatures greater than 2000° F. (1093.33° C.). In the example of FIG.1 , the component 20 is a blade or vane for a turbine. However, in otherexamples, component 20 can be another part of a gas turbine engine, suchas a combustor panel, a blade outer air seal, or another type ofcomponent.

CMC component 20 includes ceramic reinforcements 22, such as fibers,embedded in a ceramic matrix material 24. In the example of FIG. 1 , thefibers 22 are arranged unidirectional with respect to one another.However, in other examples, the fibers 22 can have other orientations,or have random orientations. In a particular example, fibers 22 aresilicon carbide fibers and matrix 24 is silicon carbide as well. In someexamples, fibers 22 include a coating, such as a boron nitrideinterfacial coating.

FIG. 2 shows a method 100 of fabricating the CMC component 20. In step102, one or more preforms 26 are arranged in a reactor 28, as shown inFIG. 3 . The reactor 28 generally includes an inlet valve 29 to controlinlets to the reactor 28 and an exhaust valve 30 to control exhaust fromthe reactor 28. A vacuum pump 31 controls the pressure in the reactor28.

The preforms 26 comprise fibers 22 and are generally porous. In theexample of FIG. 3 , multiple preforms 26 are loaded to the reactor 28and are stacked, with spacers 27 separating each preform 26 fromadjacent preforms 26. In another example, preforms 26 can be arrangedwithin reactor 28 in another way. In yet another example, only a singlepreform 26 is loaded to the reactor 28. For ease of reference, a singlepreform 26 will be referred to in the foregoing description.

In step 104, a stoichiometric precursor layer 32 is infiltrated into thepreform 26, as shown in FIG. 4 . A stoichiometric material such as thestoichiometric precursor material has a ratio of atomic constituentsthat is approximately the same as the ratio of constituents expressed inits chemical formula. For instance, stoichiometric silicon carbide (SiC)has a ratio of silicon atoms to carbon atoms that is equal toapproximately one. Silicon carbide with a ratio of silicon atoms tocarbon atoms that is substantially equal to one (i.e., “stoichiometricsilicon carbide”) exhibits improved temperature and oxidationresistance, as well as high thermal conductivity and high strength andcreep resistance as compared to silicon carbide with a ratio of siliconatoms to carbon atoms that is substantially less than or greater thanone. This is partially due to improved material uniformity.Additionally, if silicon carbide has a ratio of silicon atoms to carbonatoms greater than one, the silicon carbide has excess silicon andexhibits lowered melting temperature and lowered oxidation resistance.Likewise, if silicon carbide has a ratio of silicon atoms to carbonatoms less than one, the silicon carbide has excess carbon and exhibitsdecreased temperature and oxidation resistance. Though in this example,the stoichiometric precursor layer 32 is silicon carbide, it should beunderstood that in other examples, the stoichiometric precursor layer 32is another stoichiometric material.

In one example, the stoichiometric precursor layer 32 is deposited intothe one or more preforms 26 by an atomic layer deposition (ALD) process.In a particular example an atomic layer epitaxy (ALE) process is used.An ALE process 200 is shown in FIG. 5 . In step 202, a gas 34 that isinert is provided to the reactor 28 by opening valve 36.

In step 204, the reactor 28 is then brought to a desired temperature T1and a desired pressure P1. The desired temperature T1 and pressure P1depend on selected and used precursors and the desired stoichiometricprecursor layer 32. In one example, where the desired stoichiometricprecursor layer 32 is silicon carbide, the desired temperature T1 isabout 1832° F. (1000° C.) and the desired pressure P1 is about 0.3 torr(40 Pa).

In step 206, a first precursor 38 is provided to the reactor 28 byopening valve 40. At the same time, valve 36 is closed to stop the flowof gas 34 into the reactor 28 and exhaust valve 30 is closed to keep thefirst precursor 38 in the reactor 28. In one example, step 206 isperformed in approximately ten seconds or less. The first precursorinfiltrates into and adsorbs on the surfaces of the preform 26. For thesilicon carbide stoichiometric precursor layer 32 discussed above, thefirst precursor is a silicon-containing precursor and the secondprecursor is a carbon-containing precursor. Example silicon-containingprecursors are Cl₂SiH₂, SiH₄, ClSiH₃, and Si₂H₆. Examplecarbon-containing precursors are CH₄ (methane), C₂H₆ (ethane), C₃H₈(propane), C₂H₂ (acetylene), and C₂H₄ (ethylene). However, if anotherstoichiometric precursor layer 32 is being formed, other precursorscontaining the elements of the desired stoichiometric precursor layer 32would be used. At the end of step 206, valve 40 is closed to stop theflow of the first precursor 38 into the reactor 28.

In step 208, the reactor 28 is vacuumed by vacuum pump 31 by openingexhaust valve 30 to remove excess first precursor 38 from the reactor28. In one example, step 208 is performed for approximately between tenand 60 seconds.

In step 210, a second precursor 42 is provided to the reactor 28 byopening valve 44. At the same time, exhaust valve 30 is closed to keepthe second precursor 42 in the reactor 28. During step 210, theprecursors 38, 42 form the stoichiometric precursor layer 32 (i.e., alayer 32 with a ratio of silicon atoms to carbon atoms of approximatelyone). In the example of a silicon carbide stoichiometric precursor layer32, the second precursor 42 is a carbon-containing precursor andinfiltrates the preform 26 to form the silicon carbide, such that theratio of silicon atoms to carbon atoms on the preform 26 isapproximately one. In one example, step 210 is performed inapproximately ten seconds or less. At the end of step 210, valve 44 isclosed to stop the flow of the second precursor 42 into the reactor 28.For example, silicon and carbon from the precursors 38, 42 form asilicon carbide stoichiometric precursor layer, as shown in FIG. 4 . Inone example, the first precursor 38 is the silicon-containing precursorand the second precursor 42 is the carbon-containing precursor.

In step 212, the reactor 28 is vacuumed by pump 31 by opening exhaustvalve 30 to remove the second precursor 42 from the reactor 28. In oneexample, step 212 is performed for approximately between ten and 60seconds.

Steps 206-212 can optionally be repeated one or more times to build upthe stoichiometric precursor layer 32.

Referring again to FIG. 2 , in step 106, the component 20 is densifiedby depositing matrix material 24 onto the stoichiometric precursor layer32. The matrix material 24 is the same material as the stoichiometricprecursor layer 32. The stoichiometric precursor layer 32 favorsimproved yield and deposition of a generally stoichiometric matrixmaterial 24 in step 106. This is because reactions occurring at thesurface of the preform 26 tend to mimic the existing surface chemistryof the stoichiometric precursor layer 32 to mitigate the stackingfaults. Therefore, the matrix material 24 is generally stoichiometricand exhibits improved properties as described above.

In one example, steps 104-106 are repeated one or more times. Forinstance, after partially densifying the preform 26 in step 106, theratio of the constituents of the matrix material 24 is determined viax-ray or another type of spectroscopy in optional step 108. Then, theratio of constituents is compared to the stoichiometric ratio in step110. If the ratio differs from the stoichiometric ratio, anotherstoichiometric precursor layer 32 is infiltrated into the preform 26 asin step 104. The preform 26 is then densified again as in step 106. Thefurther densification results in a generally stoichiometric matrixmaterial 24 as described above.

In one example, the densifying in step 106 is performed by a chemicalvapor infiltration process 300, as shown schematically in FIG. 6 .

In step 302, the reactor 28 is brought to a desired temperature T2 andpressure P2. For example, for the deposition of silicon carbide matrixmaterial 24 with precursors methyltrichlorosilane (MTS) and hydrogen(H₂), as will be discussed below, the reactor is brought to atemperature T2 of approximately 1922° F. (1050° C.) and a pressure P2 10torr (1333.22 Pa). In another example, the temperature T2 in process 300is greater than the temperature T1 in process 200, and the pressure P2in process 300 is greater than the pressure P1 in process 200.

In step 304, one or more matrix material precursors 46 a, 46 b areprovided to the reactor 28. Exhaust valve 30 remains open to allow forcontinuous flow of matrix material precursors 46 a, 48 b through thereactor 28, as shown by arrows F. For a silicon carbide matrix material24, example precursors 46 a, 46 b are methyltrichlorosilane (MTS) andhydrogen (H₂). In this example, during step 304, MTS breaks down intogaseous CH₃ and SiCl₃ free radicals 50, as shown in FIG. 7 , whichadsorb onto the stoichiometric precursor layer 32 to react for theformation of silicon carbide deposit, in generally stoichiometricamounts to create a generally stoichiometric silicon carbide matrixmaterial 24. Step 304 is performed until a desired density of thecomponent 20 is achieved.

In one example, MTS is provided to the reactor 28 by opening valve 48and hydrogen is provided to the reactor 28 by valve 36, the same valvethat controls flow of inert gas 34 to the reactor 28. In anotherexample, a separate valve is used for hydrogen or another matrixmaterial precursor.

In step 306, the reactor 28 is purged by closing valve 48 to stop theflow of matrix material precursor 46 a into the reactor 28 and providinginert gas 34 to the reactor 28 via valve 36. In step 306, the reactor 28is also cooled.

Though steps 104 and 106 are described above as being performed in thesame furnace, in another example, steps 104 and 106 can be performed inseparate furnaces.

Furthermore, the foregoing description shall be interpreted asillustrative and not in any limiting sense. A worker of ordinary skillin the art would understand that certain modifications could come withinthe scope of this disclosure. For these reasons, the following claimsshould be studied to determine the true scope and content of thisdisclosure.

What is claimed is:
 1. A method of fabricating a component, comprisingthe steps of: depositing a stoichiometric precursor layer onto apreform; and densifying the preform by depositing a matrix material ontothe stoichiometric precursor layer, wherein the matrix material is thesame material as the stoichiometric precursor material.
 2. The method ofclaim 1, wherein the preform comprises silicon carbide fibers.
 3. Themethod of claim 1, wherein the stoichiometric precursor layer is siliconcarbide, and wherein a ratio of silicon to carbon in the stoichiometricprecursor layer is approximately one.
 4. The method of claim 3, whereinthe matrix material is silicon carbide and has a ratio of silicon atomsto carbon atoms, and the ratio is approximately one.
 5. The method ofclaim 1, wherein the step of depositing the stoichiometric precursorlayer onto the preform is accomplished by an atomic layer depositionprocess.
 6. The method of claim 1, wherein the step of densifying thepreform is accomplished by a chemical vapor infiltration process.
 7. Themethod of claim 1, wherein the matrix material comprises one or moreconstituents, and further comprising the steps of: determining a ratioof the one or more constituents to one another; and comparing the ratioto the stoichiometric ratio of the matrix material.
 8. The method ofclaim 1, wherein the depositing step and the densifying step areperformed in the same reactor.
 9. The method of claim 2, wherein thesilicon carbide fibers have a unidirectional orientation with respect toone another.
 10. The method of claim 1, further comprising repeating thedensifying step.
 11. The method of claim 1, further comprising the stepof repeating the depositing step.
 12. The method of claim 7, furthercomprising repeating the depositing step.
 13. The method of claim 1,wherein during the densifying step, the matrix material mimics thesurface chemistry of the stoichiometric precursor layer.
 14. The methodof claim 1, wherein the depositing step is performed at a firsttemperature, and wherein the densifying step is performed at a secondtemperature greater than the first temperature.
 15. The method of claim1, wherein the depositing step is performed at a first pressure, andwherein the densifying step is performed at a second pressure greaterthan the first pressure.